This invention pertains to movable storage systems wherein a series of storage units having shelves or bins are supported on wheeled carriages to provide for moving the units on tracks to create an access aisle between any two of the units and to establish the others in close side-by-side relationship to minimize the amount of floor space required for the units. There is a reversible electric motor mounted on each of the storage units so the units can be driven in either direction along the tracks. In particular, the invention resides in a new limit switch assembly which is capable of governing the time at which acceleration and deceleration of the units occurs as they are moved in series to close a presently open aisle and to thereby create the space for opening a presently closed aisle between units.
Details of the electrical controllers which are mounted on the individual movable storage units and a more extensive description of all of the structural and operating features of a mobile storage system are described in U.S. Pat. No. 4,759,592 whose entire disclosure is incorporated herein by reference. The patent is owned by the Assignee of this application.
Storage unit systems customarily have several mobile storage units arranged to run on tracks between two spaced apart stationary storage units. The number of mobile storage units in the system is usually one less than the number which would be required to fill all of the space between the fixed storage units so that there is always one open aisle in existence which can be entered by a person to gain access to shelves on storage units adjacent each side of the aisle. It is customary to have manually operable push button switches mounted to the upright end walls of the storage units such that when opening of a particular aisle is desired, the user will press one of the push buttons immediately adjacent the aisle which is closed and is to be opened. In the more advanced mobile storage unit systems such as the one described in the patent mentioned above, pressing the push button issues a command signal which is interpreted by a microprocessor in a controller on each of the mobile storage units in a manner that determines which way the storage units should be driven in sequence to close the open aisle and open the presently closed aisle. Typically, the mobile storage unit which is adjacent the open aisle will be the first one to begin moving toward closing that aisle. According to the prior practice, the first unit to move would have to move a substantial distance before the second unit would begin to move and there would be subsequent corresponding delays from unit to unit so that the time required to close one aisle and open another by shifting the mobile units therebetween was not minimized. The fact that the aisle opening time is not minimized in the prior art is a consequence of the type of limit switches which have been used to stop movement in response to a moving unit butting against a stationary unit. Typically, single pole limit switches were used. A spring biased rod usually extends outwardly from the switch housing into an open aisle, for instance, such that when the first movable unit adjacent the open aisle approaches a stationary mobile storage unit or a unit at the end of the series of mobile units, the rod strikes a stop on the stationary unit and begins to retract into the limit switch. When the rod is retracted against the force of the spring sufficiently far, an actuator on the rod actuates the limit switch, that is, it opens the limit switch and brings about deenergization of the driving motor on that particular storage unit. Usually the moving unit coasts for a short distance after the limit switch opened.
The prior art limit switch operating rod on the mobile storage unit adjacent the open aisle would, of course, extend into the free space between this first unit that would have to be moved and a stationary unit. With the operating rod extended, the limit switch on the first unit adjacent the open aisle would be in closed circuit condition so that it could move in response to the controller on this unit interpreting the signal produced by the use of the push button next to the closed aisle as a command to start moving all of the mobile units in the appropriate direction to close the open aisle and open the closed aisle. Of course, all of the limit switch operating rods on the storage units which trail the first unit that is to be moved toward the open aisle are extended initially which means that their limit switches were in open circuit condition so as to prohibit movement until the unit in the forward direction moved far enough away from the next succeeding unit to allow the operating rod to extend and dispose the successive limit switches in closed circuit condition. Thus, according to prior practice, when a command occurred that would cause the units to move sequentially in the proper direction to close an aisle and open another one, the first unit adjacent the open aisle had its limit switch in condition for it to begin moving in the proper direction to close the aisle. The first unit would experience an acceleration interval and then get up to full speed and finally stop when the limit switch was actuated. The first unit had to complete the acceleration interval before the unit moved far enough away from the next trailing unit to permit its limit switch to close and begin an acceleration interval. Usually the first unit would have to move about 4" before the next trailing unit would begin to move and this kind of delay accumulated all the way down the line to the last unit that would begin movement adjacent the place where an aisle was to be opened. Thus, the gap between units was substantial and total time for opening an aisle was not minimized.
Besides the delay that occurred in making the moves to open and close aisles when prior art limit switches are used, another undesirable feature is that the storage units start and stop abruptly rather than smoothly and inconspicuously as users of the equipment would desire.